Electromagnetic transducer head assembly



1386- 1951 D. E. WIEGAND ELECTROMAGNETIC TRANSDUCER HEAD ASSEMBLY 5 Sheets-Sheet 1 Filed Dec. 24, 1947 ZZWYETZZDF DAV/p E. WIEGAND.

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ELECTROMAGNETIC TRANSDUCER HEAD ASSEMBLY Filed Dec.- 24, 1947 5 Sheets-Sheet 2 IIAGNETIC RECORDER AND REPRDDUCER ssl Dec. 25, 1951 D. E. WIEGAND 2,580,208

ELECTROMAGNETIC TRANSDUCER HEAD ASSEMBLY Filed Dec. 24, 1947 a Sheets-Sheet s wz a 429 Ala [/8 [Z9 1.7725211 Zzrr DAVID E .W/EGAND.

Patented Dec. 25, 1951 ELECTROMAGNETIC TRANSDUCER HEAD ASSEMBLY David E. Wiegand, Villa Park, Ill., assignor to Armour Research Foundation of Illinois Instituie of Technology, Chicago, 111., a corporation of Illinois Application December 24, 1947, Serial No. 793,729

Claims.

My invention relates to magnetic recorders and has for its principal object the provision of an improved electromagnetic transducer head assembly for use therein.

In one method of magnetic recording, a lengthy magnetizable medium is drawn across an electro magnetic transducer head assembly at uniform linear velocity. The head assembly includes a magnetic core member having an air gap over which the medium passes and which is provided with suitable current conducting exciting elements to produce a magnetic field across the air gap.

During recording operations, current is caused to flow in the exciting elements in accordance with the time variations of an intelligence to produce a time-varying magnetic field in the core in accordance with the value thereof. Since the field fringes at the air gap portion of the core, the lengthy magnetizable medium partakes of this field as it is drawn thereover, and magnetization is imparted to incremental lengths thereof in accordance with the time variations of the intelligence, thus causing variations in the magnetization of said medium along its length in accord with the time variations of the intelligence.

During reproduction, the lengthy magnetizable medium is drawn across a similar head assembly to cause flux in the core portion thereof in accord with the magnetization of the medium at the incremental length thereover. The resultant time-varying flux induces voltage in the coil encircling the core in accord with the time rate of change thereof, which voltage may be amplified and suitably reproduced by a loud speaker or similar device to reproduce the intelligence recorded.

v Inasmuch as magnetic recording and reproducing inherently involves the conversion of an intelligence to a time-varying magnetic field during the recording operation, and conversion of a time-varying magnetic flux to an intelligence in the reproducing operation, it is of utmost importance that the mechanism provided for this purpose be free from effects due to stray magnetic fields. Frequently, for example, the transformers used in conjunction with the recording and reproducing apparatus or the induct on or other A. C. motors used therein produce stray magnetic fields which operate to produce annoying hum in the audible output of the apparatus. In accordance with my invention, this hum, together with any other disturbances associated with stray magnetic fields, are overcome by suitable balancing means and in a head mechanism that is simple in construction and reliable in operation.

Moreover, it is frequently desirable in a magnetic transducer head assembly to provide a mechanism having a large impedance ratio, to the end that the unit may be effectively connected to a high impedance circuit as, for example, the grid-cathode space path of a vacuum tube.

It is, therefore, a general object of the present invention to provide an improved electromagnetic transducer head assembly for a magnetic recorder.

A further object of the present invention is to provide an improved electromagnetic transducer head assembly for a magnetic recorder and in which the elements are so disposed as inherently to balance out the effects of any stray magnetic fields.

Further, it is an object of the present invention to provide an improved electromagnetic transducer head assembly for a magnetic recorder in which the impedance of the windings may be selected at will, and in which a simple and readily assembled secondary winding assembly is provided while at the same time, the effects of stray magnetic fields are eliminated.

Still another object of the present invention is to provide an improved electromagnetic transducer head assembly that is efficiently operable in conjunction with high impedance circuits.

Another object of the present invention is to provide an improved magnetic recorder in which apparatus producing stray magnetic fields may be used but without affecting the operation thereof.

My invention further resides in features of construction, combination and arrangement, whereby an improved head assembly for magnetic recorders in which the effects of stray magnetic fields are balanced out and which is of simple construction suitable for mass production, to the end that a unit of maximum utility may be provided.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof will best be understood by reference to the following description taken in connection with the accompanying drawings in which:

Figures 1, 2 and 3 are side elevational, end elevational and top plan views, respectively, of one embodiment of the present invention;

Figure 4 is a fragmentary cross-sectional View through the axis IVIV of Figure 3, showing the bridge portion and core portion of the assembly of Figure 3;

Figure 5 is a cross-sectional view through the axis V-V of Figure 4, showing the head core member and the disposition of a lengthy magnetizable recording medium passing thereover;

Figure 6 is a schematic circuit diagram of a magnetic recorder and'reproducer operably con- 5 nected to the electromagnetic transducer head of the present invention;

Figures '7 and 8 are top plan and side eleva'- tional views, respectively, of a further embodiment of the present invention; and" Figures 9 and 10 are top plan and side elevational views, respectively, of still another embodiment of the present invention.

As may be seen in the views of Figures 1, 2 and 3, the head assembly of the present invention includes a transformer core-'portion. I81 of: siliconz steel or similar material and which is of .rectangue lar shape having window 2! todefinea pair of aligned legs 22 and 24. A coil or windingindicate'd generallyatzfi encircles the-core Is;- this coil" being divided in two-portions- 2621 and" 26b" having-like-numbers of 't'urns and" which encircle the alignedlegs 22 and 2 1, respectively. Conducting sleeves 28 and Eliaremounted outwardly of the coil 26?; and 26b,'respectively, andare-sus' tained thereon by the insulating-spacers 29 which are mountedabout the periphery of 'the=coi1 26-"as is'bestseen in Figure- 3, and" which snugly fit between that coil and the sleeves 28 and 3B.

The sleeves-28 and 36' are mademf'copper or like conducting material and, as seen best in Figure' 3; each nearly encircles the-corresponding leg; ZZ an'd 24, respectively, sleeve ZBhavingan arcu ate open portion defining the confronting-edge portions 618d and 281), Figure 3, and theslee-ve =31! having a similar arcuate open portiondefining the confrcntingedge portions 30a and 30b, Figure 3;

The arcuate open'portions of'thesleeves ZB-and 3'0 'areon the'same side of the -core=l8 and par tially face each other. The confrontingend' por tions 28a" and 30aare interconnected by the U -.shaped conducting member 3Z'which-hasa pair of turned-out fl'angesSZiz and 32b'forconnection to the sleeves 28 and 36; respectively, by soldering or like'means: Similarly, the "conductingmember'34'has turned-in end portions connected to o the edgenortions 28b and 3fib of the sleeves 28 and 30, respectively.

The conductingv members 32 and 34 are constructed of copper or like conducting material and extend. across a substantial portion of the length of the sleeves 28 and.3ll, .asmay'be'seen in the view of Figure 1, thus defininga low resistance current path in conjunction with the sleeves. As indicated by the dotted .lines of'Figure 1 and the view of Figure 5, the. member 34 is of'like length axially offthelegs. 22 andl24 as is the member 32. At their central portions, the members 32and 34 define spaced parallelconductors to receive the head core member 36;. A con-.- ducting. bridge 38' extends. between the members 32 and-3.4 andis receivedin the. core 36'to.pro= duce flux therein in accordiwithvcurrent fiow therethrough.

The construction of the. bridge 38,. together with the core 36 is best seen in the views of Fig.- ures l and 5. As seen in the view of Figure 4; the conducting bridge 38.is.of rectangular. shape and is received at its opposite. ends. in slots in the members 32and34. In order-to accomplish a good path'for current conduction. between the bridge 33 and the members 32. and. 34; the bridge 38 is preferably brazed to these members astindicated by-thebeadg 3 and 33 Figurea As shown in Figure 5, the bridge 33 is relatively thin and is received in a slot 36a of the core 36. This slot also defines the air gap across which a lengthy magnetizable medium 42 is drawn. This core is of substantially rectangular shape with a rounded ofitop portionz3fib;,the slot 36a extending from that top portion down approximately to the center of the core 36.

The bridge 38 is positioned relative to the sleeves 28. and 30, and the members 32 and 34 to divide'the current path defined thereby into two symmetrical halves. This is seen best in the view of Figure 3.-

It will be apparent to those skilled in the art thatwhen' currentfiuws through the bridge 38 in direction transverse to the plane of cross-sec tionoiFiguraS; .amagnetic field is set up about the bridge 38 and results in magnetic flux being developedin core 36 following a, closed path such as that generally indicated at 4!]. Moreover, this current flow produces amagnetic field across the air gap:d'efined by thetgroove 3 6a; the-11112611 sity of this magnetic field i being determined by the reluctance of the magnetic path defined by tensity of current flow through the bridge 1 33;- Since the core'3'fi is preferably constructedlcfi iron having a" high magnetic permeability; and the slot 36'a-is narrow; the intensity of the mag netic field across the gap defined by the slot' 3fia is relatively'great, particularly 'at the'en'd por tions thereof adjacent the edgefi'fibof the core 36.

The upper edge 3% of "the core 3fi' is rounded to' receive a lengthy magnetizable recording me dium such as, forexampl'e, a fihe steel wire: A groove'or slot'36c; Figures 2and '3', is formed' in this edge ofthecore and, as shown'inFigures l and 5, receives the'lengthy magnetizable medium 42. The conducting membertl'is-provided with a pairof' V-shapednotches-32cand 3211, Figure- 3, to provide space for the passage of the record medium through the'assembly'.

Inthe figures;.the medium 42 is shown-greatly enlarged*to.:illustrate clearlyhow it rests on the headcore 36i Actually; this medium is best made ofivery fine-material, such as, forexample, steel wire four mils in diameter: Moreover, thewidth of the bridge 3'8 and 'the'slot 36a 'in' which it iS'16-' ceived is greatly exaggeratedto'illustrate'clearly. the arrangement of theparts, and in an" actual embodiment; this .width is preferably made very small such as, for example, less than one mil."

The operation of the structureofjFigures rto, 5. may, best-be. unclerstoodbyv the. schematic. dia: gram of Figure 61 For purposes of identification... like. elements onlthe structure. of Figures. 1,. to 5 are identifiediwith likenumberson Figure 6. As indicatedrinsFigure 6, the coil ZE-is connected-to thev magnetic. recording, and. reproducing unit 44... This-.unit contains elements t'o convertsin telligencesuch as sound,qfor. example, to altimevarying voltagewhich isimpressed across-theacoil 25. During the. reproducing operation; the-rev corderand; reproducer, 44 includes; elements to convert theatime-varying voltage. in coil 26, to the originalintelligence. suchas, for example; sound.

Itwill be observedthat as the-conducting path includingthe recorder 54' and the coil-2i; is trav' ersed in a single. direction as, for example; the pathindieatedby' the arrowssfi; the leg 22 of core l8;.-.is encircled in anoppositedirection-.110 the leg 2 h.- Accordingly; current flow incoiliifiiase sociated' with voltage; produced by; the. recorder i l causes oppositely directed fluxes to be developed in the core portions Eric and 26b as indiauaazoa cated by the arrows 48 and 50, respectively. Since -these fluxes or magnetomotive forces are in like direction and additive relationship as the core I8 is traversed, the total flux produced therein, is that associated with the combined operation of these coils. The sleeves. 28 and 38, which are represented by corresponding turns on the legs 22 and 24 of the core I8, also link the flux produced by current flow through the coil 26. Voltages are induced in these sleeves tending to cause current flow therethrough, this current flow being in direction to pass through the bridge'38, represented by a resistance, in Figure 6, in like direction as indicated by the arrows 52, 54 and 56, Figure 6. The bridge 38 is indicatedby a resistance, since it is of relatively great resistance as compared to the resistance of the other portions of the circuit. Current flow in the bridge member 38 produces magnetizing magnetomotive force as is shown in Figure 5.

It will be observed that stray flux such as, for example, might be directed in direction of the arrow 58, Figure 1, has no effect on the voltage produced across the bridge member 38, even though the direction of the flux 58 has a component in alignment with the windings 2S and the sleeves 28 and 30. Such flux produces like fiuxes in the opposite legs 22 and 24 of the core I8. However, these fluxes produce additive voltages in the sleeves 28 and 30 as the latter are traversed through the path including sleeve 28, member 32, sleeve 30 and member 34. However, since these sleeves are of like resistanceand impedance, and the bridge 38 is symmetrically disposed relative to members 32 and 34, there is no tendency for a voltage to be produced across the bridge member 38 as a consequence of this flux.

Moreover, when the unit is used as a pick-up to produce voltage for application to the restray fields, and such fields can produce no annoying hum or other effects on the operation of the complete unit.

In one application of the head assembly of the present invention, the magnetic, recorder may include a power transformer to supply the necessary operating voltages for tubes and other equipment, and induction drive motor to impart linear velocity to the lengthy magnetizable medium. Although both of these have some tendency to produce stray fields, and hence induce hum in the reproduced output intelligence, they may be mounted with assurance that no effect will be produced on the operation of the unit if the head assembly of the present invention is employed.

Figures 7 and 8 are top plan and side elevation views, respectively, of an alternative embodiment of the present invention. As indicated in these views, two core members, H8 and II8a, each like the core member I8, Figure l, are provided and are sustained in spaced relationship relative to each other by suitable mounting arms H8. A coil I26 encircles the legs of core H8, and a coil I 26a encircles the legs of core ll8a. Sleeves I28, I38, I28a and BM encircle the coils iii.

I28 and I28a in like fashion as do the sleeves 28 and 30, Figure 3. Sleeves I28 and I38 are held in position by the insulating spacers I28, and sleeves I'28a and I30a are held in place by the insulating spacers I28a. Each sleeve has an open arcuate portion facing the space between cores H8 and Ba.

The sleeves I28, I38, I28a and I38a are connected by the conducting members i354, I32, I34a and I32a, which are of construction similar to the conducting members 32 and 33, Figure 3, except that they are shaped to provide suitable mounting flanges for connection by soldering or like means tothe sleeves I28, I30, I3Ga and I28a. A head core member I36, like the core member 36, Figure 3, is nested in the space defined by the members I34 and IBM and is provided with a suitable groove to receive the conducting bridge I38.

The core I36 is like the core 38 in that it has a groove I36a at its top surface to receive a lengthy magnetizable medium and receive the bridge I38 in a suitable slot to cause a magnetic field to operate upon an incremental length of the medium disposed in the slot I3Ea in accord with the current fiow through the bridge I38.

It will be apparent to those skilled in the art that the unit of Figures 7 and 8 operates in like fashion as the unit of Figures 1 to 5. However, the current paths through the bridge E38, Figure 7, link two legs I22 and I22a or 24 and I2 ia, whereas the current paths through the bridge 38, Figure 3, link only a single leg 22 or 24.

The coils I26 and I28a which encircle the legs of the cores H8 and H811 are wound in like fashion as the coil 26, Figure 3. These coils ar connected in additive series relationship for connection to a magnetic recorder and reproducer in the manner indicated in Figure 6 so that the total voltage applied thereto is the combined voltage induced in coils I26 and I26a during the reproducing operation and the voltage of the recorder is impressed across the combined series of coils during recording. Since the bridge I38 is disposed to divide the circuit of the sleeves I28, I38, I28a and I38a into two symmetrical halves, the unit is hum-bucking in both the primary and secondary circuits, and no voltages are induced in the unit by stray magnetic fields.

The connection of the coils I26 and I26a is such that upon current flow therethrough, flux is produced in one direction in legs I22 and I22a and in the opposite direction in legs I24 and I24a.

The structure of Figures 9 and 10 is like that of Figures 7 and 8, except that the coils I28, I38, I30a and I28a are connected in a parallel connection in which the voltage produced in each coil is impressed across the common bridge I33. This is accomplished by the criss-cross conducting members 232 and 233 and 232a and 233a. These members may be seen in side view in Figure 10.

The structure of Figures 9 and 10 provides an increased impedance ratio between the primary and secondary windings, since the net efiect of the sleeves I28, I30, I30a and I28a in that structure is to produce a single-turn secondary.

Elimination of the eifects of stray fields in the apparatus of Figures 7 to 10 is further improved by the fact that the head core I38 is nested between the transformer cores I18 and H811.

In the foregoing specification and in the appended claims I have defined the head core 36 as having an air gap 38 to receive or to be trav- 7 ers'ed" bythemefdium; 'Bythis'expression I intend to include: construction such as that of Figure dwhere the 'airgapfiux actually passing through the medium is fringing or leakage flux as 'distinguishedfrom the direct flux passing in a straight line 'across the'air gap;

While I have shown particular embodiments of my invention, it will, of course, be understood that I do not wish to be limited thereto since many modifications, both'in the circuit arrangements and in the structures disclosed, maybe made without departing from the spirit and scope of my invention.v I, of course, contemplate by the appended claims to cover'any such modifications as fall within the true spirit and scope of my invention. r

I claim as my'inve'ntion:

1. An electromagnetic transducer head assembly including at least one core having a pair of aligned le'gs, means for producing oppositelydi ected magnetic fields on said legs; a conductingsle'eve partially encircling e'achof said legs, spaced conducting members joining the open ends of the sleeves, a conducting bridge electrically interconnecting said conducting members to form parallelcon'ductive circuits; and a magnetic core member substantially'encircling said bridge and having a non-magnetic gap across which a lengthy magn'etizable medium may be drawn.

2. An electromagnetic" head assembly including a rectangular core having; an opening there through to define" a pair of aligned legs, means for producing oppositely directed magnetic fields on said legs, a conducting sleeve partially en'- circling each of said legs, spaced conducting mem bers electrically interconnecting the sleeves in series circuit relationship, aconducting bridge electrically interconnecting said members, and a magnetic core member substantially encirling said bridge and having a non-magnetic gap across which a lengthy magnetizable medium may be drawn.

3. An electromagnetic transducer head assembly including a core having a pair of aligned legs',. means for producing oppositely directed magnetic fields on'said legs, a conducting sleeve partially encircling each of said legs; conducting members electrically interconnecting the sleeves, a conductor electrically interconnecting I said conducting members, and a magnetic core member substantially encircling said conductor and having a non-magnetic gap across'which a lengthy magnetizable medium may be drawn.

4. An electromagnetic transducer head assembly including a core having a pair of aligned legs, means for producing oppositely directed magnetic fields on said legs, a pair of conducting sleeves substantially encircling said legs and having open portions facing on a common side of said 4 may traverse and means including a conducting bridge symmetrically positioned relative to said sleeves and electrically connecting'said conduct ing members, said bridge being substantially encircled by said core to produce a magnetic field across said gap upon current flow therethrough.

5. An electromagnetic transducer head as'sem' bly including a corehaving a'pair of'aligned legs, means for producing oppositely directed magnetic fields on said le'gs,'a pair of conducting sleeves substantially encircling said legs and having open 'portions facing on a' common side of said core, a conducting member 'conn'ectin'g the edges of said sleeves closest to each other, a second conducting member in spaced relationship with said first conducting member and connecting the edges of said sleeves most remote from each other, a 'core member defining a head for said transducer disposed between said conducting members and having a non-magnetic gap across which a lengthy magnetizable medium may be drawn and a conducting bridge sym= metrically positioned relative to said sleeves and extending therebetween, said bridge being encircled by said head core to produce a magnetic field across said gap upon current flow therethrou'gh.

6. An electromagnetic transducer head assemcly including a rectangular core having an opening therethrough defining a pair of aligned legs, means for producing oppositely directed magnetic fields on said legs, a pair of conducting sleeves substantially encircling said legs and having open portions facing on a common side of 'said core, a first conducting member connecting the edges of said sle'eves'closest to each other, a second conducting member in spaced relationship with said first conducting member and connecting the edges of said sleevesrn'ost remote from each other, a core member defining a head for said transducer disposed between said conducting me'm' bers,fsaid head core member having a nonmagnetic gap across which a lengthy magnetizable medium may be drawn, and a conducting bridge encircled by said core symmetrically positioned relative to said sleeves and electrically connecting said conductors to produce a magnetic field across said gap upon current fiow therethrough. 7. An electromagnetic transducer head assembly including a rectangular core having an opening therethrou'gh defining a pair of aligned legs, means for producing oppositely directed magnetic fields on said legs, a pair of conducting sleeves substantially encircling said legs and having open portions facing on a common side of said core, a first conducting member connecting the edges of said sleeves closest to each other and attached thereto along a substantial portion of the axial length thereof, a second conducting member in spaced relationship with'said first "conducting member and connecting the edges of said sleeves most remote from each other and attached there'- to along a substantial portion of the aXial length thereof, a core member defining a head for said transducer of substantially rectangular shape disposed between-said conducting members, said head core member having one edge" thereof slotted to receive a lengthy "magnetizable" me"- dium and having a lengthy slot extending inwardly from said edge, and a conducting bridge symmetrically positioned relative to said sleeves andconnecting said conductorsthrough said slot of said head core member.

8. An electromagnetic transducer head assembly'including a pair of spaced ooreseach having two aligned legs, Wirdings encircling the flux paths defined. bysaid cores to produce fluxes traversing two of said legs in one direction and the other two of. said legs in opposite direction upon current flow through said windings, conducting sleeves substantially encircling each of said legs and having open portions facing the space between said cores, conducting members attached to the edge portions of said sleeves and defining a series current path therewith encircling each of said legs in a common direction, a core member defining a head for said transducer having a non-magnetic gap to be traversed by a lengthy magnetizable medium, and means including a bridge of electrical conducting material connecting opposite portions of said conducting members to define a pair of symmetrical loops therewith, said bridge being electrically connected with and substantially encircled by said head core to cause a magnetic fieid across said gap in accord with the current flow therein.

9. A head assembly for a magnetic recorder including a pair of spaced cores each having two aligned legs, windings encircling the flux paths defined by said cores to produce fluxes traversing two of said legs in one direction and the other two of said legs in the opposite direction, conducting sleeves substantially encircling said. legs and having open portions facing the space defined by said cores, a core member defining a 25 head for said transducer nested between said cores and having a non-magnetic gap across which a lengthy magnetizable medium mey be drawn, a conductin member electrically connected with said head core member and encircled thereby to cause an electromagnetic field across said gap in accord with current flow in said conducting member, and conducting elements connecting the edges of said sleeves to said conducting member, said elements defining at least two physically symmetrical loops in conjunction with said conducting member.

10. An electromagnetic transducer head assembly including at le: st one core havin a pair of aligned legs, means for producing oppositely directed magnetic fields along said legs, conducting sleeves partially encircling each of said legs, spaced conducting members electrically interconnecting said sleeves into a circuit, conducting bridge means interconnecting said members, and a core member substantially encircling said bridge defining a head for said transducer having a gap therein across which a lengthy magnetizable medium may be drawn.

' DAVID E. WIEGAND.

No references cited. 

